Capillary fluid transmission system



Dec- 6, 1932- D. D. RosENBURGH 1,889, 792

' DURWOOD I). ROSENBURGI-I, OF ROCI-IESTER, NEW YORK, ASSIGNOR' itype disclosed in the patent to Patented Dec. 6, 1932 UNITED sTATEs PATET- ort-fier:

TO TAYLOR INSTRU- IMIENTL COMPANIES, OF ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK CAPILLARY FLU'ID TRANSMISSION SYSTEM' Application filed October 19, 1926. Serial No. 142,632.l

This invention relates to instruments including a capillary flui-d transmission system and more particularly to apparatus of the Hodgkinson No. l,'063,349 dated June 3, 1913.

It has been generally recognized as a desideratum to reduce the size of the capillary for transmittingthe fluid pressure from the hulb to the pressure element so far'as this is compatible With the pressure requirements at the latter. I V

vAside from the point of cost, there is another even more cogent reason for reducing the volume of .the transmitting liquid, or mercury in particular, to a practical minimum: Mercury, for instance, has a. high coefficient of expansion. Changes in the temperature surrounding the transmission sysi tem cause a change in the volume of the transmitting liquid, with the result that this expansion or contraction, as the case may be, reacts upon the pressure condition in the pressure responsive element, which pressure condition should be and is intended to be solely a vfunction of the changes in the volume of the 'liquid in the -bulb in response to changes of the temperature conditions to Which the bulb is *subjected The greater the volume -ofithe transmitting liquid, the greater is the influence of changes in its temperature upon :the indication ofthe instrument; In all 'cases where the transmission system is subjeoted to material Variations in temperature it is necessary to compensate for the dchanges in the volume of .the transmitting fluid caused thereby.

ompensation may be obtained to a certain extent hy using a 'filler wire, such as disclosed in the patent mentioned, of a material having a smaller co-efiicient of expansion than the material of the capillary tube. Due to the differential expansion and contraction the Variable interspace between the wire core and the walls Iof the-tube thus may have a compensatory effect for the Variations in the volume of the transmitting liquid. Ho-wever, the compensation aiforded is, in the usual case, 'not entirely zsatisfactory.

It is the primary object of this invention to provide a simple transmission system which may afford complete "compensation. Another, more general object is to produce a transmission conduit having a substantially uniform cross-sectional area.

Still another particular object-is a method of forming a. capillary transmission systeml are comparatively irregular. The diameter as awhole varies Within wide limits and'there are many deformations, such as furrows, depressions and other cavltles, all tending to increase the interspace and thereby the vol-v ume of the transmittingliquid. In addition to these cavities Which directly increaseA theV interspace, there are rough spots distributed:

along the Walls of the capilliary, all having the tendency to impede or obstruct the passage of the wire through it. The largest wire which may be fed into any tube is considerably smaller in diameter than the bore. It is thus practically impossible to enter a filler core of less than .006 difference in diameter.

All these inconveniences and disadvanffs tages may be overcome by my invention,

which, briefly expressed, consists in drawing or swaging a tube down upon a core to any desired extent.

For a full understanding. of the invention, reference is made to the .accompanying drawing in which Fig. l is a. diagrammatic view of an instrument embodying the invention;

Fig. 2 is a sectional view on a. relatively large scale, of a tube and a wire in assembled relation prioryto the drawing or swaging operation; i v

vices adapted to operate under fluid pressure.

and 3 is a capillary transmission system.

In practice I select a wire 3a, which has substantially the desired diameter and then enter it into a tube 31) sufficiently larger in boreso as to readily pass into and through it. In fact, the clearance between the walls of the capillary and the core may be considcrably larger than the usual tolerance, because the tube is to be reduced in size any Way. However, as a matter of common sense, in order to avoid all unnecessary waste of energy and expense, it is preferable to use a wire which 3just readily enters the tube or a tube which just slips over a core. In this way the operation of entering the Wire into the tube does not consume much time and at the same time, the amount of drawing or swaging required 3? is reduced to a relatively small amount.

With the wire in position in the tube, the latter is drawn or swaged upon it. The drawing or swaging operation may be conducted and controlled to obtain any desired degree of fit, as willbe readily understood.

However, so far as the particular purpose is concerned, it is preferably so conducted as to 'leave justenough clearance to allow a film of mercury to form therein. In practice I 4311 lind that a good fit is obtained When it requires a considerable force to move the wire by pulling. So long as the wire can be moved, the interspace is ordinarily small. The capillary may be tested by forc- 43? ing air through it under a definite pressure,

say about 4 pounds per square inch, into Va body of water, and counting bubbles per unit of time. The proper setting of the drawing or swaging may be empirically determined for any size of tube and wire correlated therewith and the clearance or interspace may be varied Vfor different practical requirements, having reference to the p pressure conditions desired at the pressureresponsive element 1. e. the Bourdontube or the like. In other words the allowable pressure gradient between the two ends of the transmission line may vary between certain limits, depending also to some extentL upon r' the length of the line.

By measuring the volume of liquid in a capillary of a given length, prepared accordinO' to this invention, I found that the clearance may be made as small as .0004 and even 0002. learances lower than 0002 are,

not tooy mum. This is in contradistinction to the 1 vprior art which had to accept as the minimum clearance or interspace that which was formed by entering as large a wire as was possible. p

Not only is the general way, butL bore, the furrows,

interspacev reduced in a the irregularlties ln the depressions and cavlties which are present in tubes as unavoidable ncidents are reduced in size and extent or even more i or less eliminated. Especially the swaging operation has a peculiar equalizing effect in this respect. The result of the drawing or swaging opera-tion, aside from the net reduction in diameter, is the more particular and important leveling or smoothing out of the rough, irregular surface of the bore and the elimination of a previously unavoidable space, Which from the standpoint of operation was unneces'saryand merely required more compensation than Would have been necessary without it. V

It is needless to emphasize thata relatively smooth interspace makes it possible to obtain a minimum of resistance to flow for a minimum of volume of fluid. This translatedl into practical parlance, means that it is possible to obtain a fast instrument With a minimum of transmission fluid.i i

Whenever a vvery fast instrument is desired, the resistance to flow maybe precisely determined by the provision of a .groove 412, in the surface of the 'core 4a, as indicated in: Figs. 4 and 5. The groove may vary from a fine thin capillary thread to a groove of more 'substantial size depending upon thev speed desired; The tube is drawn or swaged upon the coreas before to eliminate substantially all the waste space and reduce the interspace to a relatively i smooth clearance space allowing a film to Iform.

Depending on the volume of mercury, the diameter of the core and the bore may be increased to obtain the difi'erential movement necessary for the accommodation of the ex-V panding mercury. Thehigher the speed i. e. the quicker the response desired, the greater must be the cross-section of the transmission conduit, and the greater is consequently the volume. of mercury. For this reason the differentialy movement must be correspondingly great and this can be easily obtained by using a core and a bore of relatively large diameter. Instead of using a wire of a diameter between .012-.015, the core may have'a diameter of .060-k.065, or even higher.

At any rate, by providing a groove in the Wire core, it is possible to precisely determine the speed of the instrument with a minimum of volume of mercury.

Instead of providing the groove in the surface of the core, it may be formed in the bore of the tube during the process of drawing. I-Iowever, I prefer to score or groove the wire core, as shown.

The invention not only has th-e advantages described, but also the outstanding commercial advantage thatit is no longer necessary to use tubes of an extremely small bore with or without wire filler. Tubes with larger bore, which are easier to make and are less expensive, are now available for the purposes described.

It is understood that in place of a solid core a tubular core may be used. I-Iowever, for practical purposes a solid core is prefyerable.

In the foregoing, the invention has been v described in the light of its principal object of producing Va wire-filled capillary. It is understood, however, that it is equally important for producing the usual form of capillary tube Without filler wire.

I claim:

1. In apparatus of the character described, a capillary tube having a uniformly smooth Vbore of substantially circular cross-section and containing a filler core of uniformly smooth surface, the difference in diameter lev'f'een the bore and the core being less than 2. In apparatus of the character described, a capillary tube having a uniformly smooth bore of substantially circular cross-section and containing a filler core of uniformly smooth surface, the difference in diameter mission systems, having a capillary bore sub- V stantially free from furrows and ridges such as are incident to the usual drawing operartion.

7. A metal capillary tubing for fluid transmission systems, having a capillary bore of uniform circular cross-section throughout its length and substantially freeV from furrows and ridges such as are drawing operation.

8. In apparatus of the character described, the combination with a bulb containing an eXpansible fluid and a device sensitive to Variations in fluid pressure, a capillary tube for interconnecting the bulb and said-device, said tube being provided with a capillary bore adapted to receive a filler core having a smooth uniform surface throughout its length, the surface of said bore having substanrtially the 'same degree of smoothness as the surface of said filler core.

9. A capillary tubing for fluid transmission systems provided with a capillary bore adapted toL receive a filler core having a smooth uniform surface throughout its length,.the surface of said bore having substantially the same degree of regularity as the surface of said filler core.

DURWOOD D. ROSENBURGH.

between the boreand the core being less than 3. In apparatus of the characterdescribed, a capillary tube having a uniformly smooth bore of substantially circular cross-section and containing a filler core of uniformly smooth surface, the difference in diameter between the bore and the corebeing no more than 0015.

4. In apparatus of the character described, the combination With a bulb containing an expansible fluid and a device sensitive to Variations in fluid pressure, of a metal capillary tube for interconnecting the bulb and the said device, said tube having a capillary bore substantially free from furrows and ridges such as are incident 'to the usual drawing operation.

5. In apparatus of the character described, the combination with a bulb containing an expansible fluid and a device sensitive to Variations in fluid pressure, of a metal capillary tube for interconnecting the bulb and incident to the usual 

